Shower plate having projections and plasma CVD apparatus using same

ABSTRACT

A shower plate  122  has protrusions  22  formed on the front face used with a first electrode in a plasma CVD apparatus. A plane-surface portion  23  is left around apertures of gas inlet holes  21  formed in the shower plate  122 . With protrusions  22  being formed, a surface area of the first electrode is increased.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a plasma CVD apparatus usedin a semiconductor manufacturing process; particularly to a shape of ashower plate provided in the plasma CVD apparatus.

2. Description of the Related Art

A conventional plasma CVD apparatus possesses a first and a secondelectrodes disposed parallel to each other inside a vacuum chamber; thefirst electrode has a hollow structure for introducing source gases intothe vacuum chamber and has a shower plate removably attached in itsbottom face; in the shower plate, many gas inlet holes are formed.

A conventional shower plate is disk-shaped and has many gas inlet holesof a given diameter being formed with an arrangement to be adapted topass completely through to the reverse face of the shower plate from itsfront face.

Additionally, as shown in FIGS. 15( a) and (b), there is a shower platehaving gas inlet holes having diameters gradually increasing to thedirection of gas flow (for example, see U.S. Pat. No. 4,854,263). Thisshower plate has larger apertures on its forefront surface in ahoneycomb-shaped surface pattern as shown in FIG. 16.

Conventional plasma CVD apparatuses have a problem in that it isdifficult to form a thin film having desired properties stably withexcellent controllability or reproducibility. That is, the operableranges to produce desired films are narrow. This problem cannot besolved even by using the shower plate of U.S. Pat. No. 4,854,263.

Additionally, the shower plate of U.S. Pat. No. 4,854,263 has anotherproblem in that its shape pattern gets to be transferred to a filmthickness distribution of a thin film formed.

SUMMARY OF THE INVENTION

Consequently, in an aspect of the present invention, an object is toprovide a plasma CVD apparatus which is able to form a thin film havingdesired properties stably with excellent controllability.

In another aspect, an object of the present invention is to provide ashower plate used in a plasma CVD apparatus, which makes it possible toform a thin film having desired properties stably with excellentcontrollability.

The present invention can accomplish one or more of the above-mentionedobjects in various embodiments. However, the present invention is notlimited to the above objects, and in embodiments, the present inventionexhibits effects other than the objects.

In an embodiment, the present invention provides a shower plate forplasma CVD comprising: (i) a base surface having multiple apertures forpassing a gas therethrough; and (ii) multiple protrusions eachseparately protruding from the base surface and being dispersed amongthe apertures.

In another embodiment, the present invention provides a shower plate forplasma CVD comprising: (i) a base surface; (ii) multiple protrusionsprotruding from the base surface, and (iii) multiple apertures forpassing a gas therethrough dispersed on a front face constituted by thebase surface and the protrusions, wherein a surface area of the basesurface and the protrusions is greater by at least 40% than a calculatedsurface area of the base surface if no protrusions are provided, andwherein a surface area when extending from the base surface and theprotrusions by a sheath generated by plasma exposure is nearly orsubstantially equal to or greater than the surface area of the basesurface and the protrusions.

The present invention also includes an aspect directed to a plasma CVDapparatus comprising: (a) a reaction chamber; (b) a showerhead providedin the chamber, which serves as an electrode and comprises the showerplate described above and a body member to which the shower plate isattached; and (c) a susceptor provided in the chamber, which serves asanother electrode and is disposed parallel to the shower plate.

In still another aspect, the present invention provides a plasma CVDmethod comprising: (1) placing a substrate on a susceptor disposedparallel to the shower plate described above; (2) introducing a reactiongas through the shower plate; (3) generating a plasma between thesusceptor and the shower plate by applying radio-frequency energytherebetween, wherein a sheath is formed over the shower plate, whereina surface area of the sheath is nearly or substantially equal to orgreater than a physical surface area of the shower plate; and (4)depositing a film on the substrate.

According to at least one embodiment of the present invention, byforming a plane-surface portion surrounding the apertures of multiplegas inlet holes and protrusions protruding from the plane-surfaceportion on the front face of a shower plate, and using a plasma CVDapparatus using the shower plate, a thin film can be formed stably withexcellent controllability.

For purposes of summarizing the invention and the advantages achievedover the related art, certain objects and advantages of the inventionhave been described above. Of course, it is to be understood that notnecessarily all such objects or advantages may be achieved in accordancewith any particular embodiment of the invention. Thus, for example,those skilled in the art will recognize that the invention may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught herein without necessarilyachieving other objects or advantages as may be taught or suggestedherein.

Further aspects, features and advantages of this invention will becomeapparent from the detailed description of the preferred embodimentswhich follow.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described withreference to the drawings of preferred embodiments which are intended toillustrate and not to limit the invention. The drawings areoversimplified for illustrative purposes.

FIG. 1 is a schematic view of a plasma CVD apparatus showing a basicstructure according to an embodiment of the present invention.

FIGS. 2( a)-(c) show an embodiment of a shower plate used in the plasmaCVD apparatus shown in FIG. 1. FIGS. 2( a)-(c) are a partial crosssection seen from obliquely upward, a partial longitudinal crosssection, and a bottom view, respectively, showing the shower plate.

FIGS. 3( a)-(c) show another embodiment of a shower plate used in theplasma CVD apparatus shown in FIG. 1. FIGS. 3( a)-(c) are a partialcross section seen from obliquely upward, a partial longitudinal crosssection, and a bottom view, respectively, showing the shower plate.

FIG. 4 is a graph showing properties (internal stress vs. high RFoutput) of a film formed by Example 1-1 of the present invention.

FIG. 5 is a graph showing properties (internal stress vs. high RFoutput) of a film formed by the related art.

FIG. 6 is a graph showing properties (internal stress vs. low RF output)of a film formed by Example 1-2 of the present invention.

FIG. 7 is a graph showing properties (internal stress vs. low RF output)of a film formed by the related art.

FIG. 8 is a graph showing properties (internal stress vs. high RFoutput) of a film formed by Example 1-3 of the present invention.

FIG. 9 is a graph showing properties (internal stress vs. high RFoutput) of a film formed by the related art.

FIG. 10 is a graph showing properties (internal stress vs. high RFoutput) of a film formed by Example 2-1 of the present invention.

FIG. 11 is a graph showing properties (internal stress vs. low RFoutput) of a film formed by Example 2-2 of the present invention.

FIG. 12 is a graph showing properties (internal stress vs. high RFoutput) of a film formed by Example 2-3 of the present invention.

FIGS. 13( a)-(c) show an embodiment of a shower plate used in the plasmaCVD apparatus shown in FIG. 1. FIGS. 13( a)-(c) are a partial crosssection seen from obliquely upward, a partial longitudinal crosssection, and a bottom view, respectively, showing the shower plate.

FIG. 14( a) is a schematic diagram explaining an increase of surfacearea with a sheath formed on a convex structure. FIG. 14( b) is aschematic diagram explaining an increase of surface area with a sheathformed on a concave structure.

FIGS. 15( a)-(b) are cross sections, respectively, showing gas inletholes formed in a shower plate of the related art.

FIG. 16 is a bottom view of the shower plate shown in FIG. 15( a) or(b).

Explanation of symbols used in the drawings are as follows: 10: PlasmaCVD apparatus; 11: Vacuum chamber; 111: Exhaust port; 12: Firstelectrode; 121: Gas inlet port; 122: Shower plate; 13: Second electrode;131: Heater; 132: Susceptor; 14: First RF power source; 15: Second RFpower source; 16: Workpiece; 21, 21′: Gas inlet holes; 22, 22′:Protrusion; 23: Plane-surface portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As described above, in an aspect, the present invention provides ashower plate for plasma CVD comprising: (i) a base surface havingmultiple apertures for passing a gas therethrough; and (ii) multipleprotrusions each separately protruding from the base surface and beingdispersed among the apertures. The base surface may be constituted by aphysical surface composed of a plane, a curved surface, or a combinationthereof, or a hypothetical surface. In this embodiment, the aperturesare provided in the base surface. Further, in this embodiment, themultiple protrusions each separately protrude from the base surface;e.g., the protrusions are discontinuous protrusions just like islands inan ocean, not like land having ponds.

The above embodiment includes, but is not limited to, the followingembodiments:

A surface area of the base surface and the protrusions may be greater byabout 20% to about 500% (including 40%, 60%, 80%, 100%, 200%, 300%,400%, and any numbers therebetween), preferably at least 40% (morepreferably 70% to 300%), than a calculated surface area of the basesurface if no protrusions are provided. In the above, to calculate thesurface area of the base surface, the areas of the apertures are notconsidered; i.e., the surface area of the base surface is calculated asif there are no apertures provided. For example, if the protrusions arehexagonal columns having a height of 3-9 mm and a width of 3 mm andprovided at a pitch of 6 mm, the surface area is increased by about 72%to about 216%.

In an embodiment, a surface area when extending from the base surfaceand the protrusions by a sheath generated by plasma exposure may benearly or substantially equal to or greater than the surface area of thebase surface and the protrusions. A sheath is a boundary region formedin front of an electrode surface when being exposed to a plasma. In thesheath, complex behavior of ions and particles in a dropped electricpotential is involved (see e.g., Brian Chapman, “Glow DischargeProcesses”, John Wiley & Sons, Inc., 1980, Chapter 3). The thickness ofthe sheath may be determined using a computer simulation (see e.g.,Onoue et al., “TCAD Simulation for Virtual Design of SemiconductorProcesses”, Toshiba Review Vol. 58, No. 6, pp. 60-63, 2003). The sheathregion is a darker region as compared with a plasma, and can be observedby eye easily. Typically, a sheath having a thickness of about 0.5 mm to1.0 mm can be observed. Further, the thickness of the sheath region maybe several times (e.g., 5-10 times) the Debye length which is less than10⁻⁴ m (0.1 mm) or less under typical surface treatment conditions. Inany event, the sheath is important to plasma surface processing.

FIGS. 14( a) and (b) are schematic diagrams explaining an increase ofsurface area with a sheath formed on a convex structure and a sheathformed on a concave structure, respectively. The difference between thesurface area of a physical surface 40, 50 and the surface area of asheath 42, 52 is attributed to a difference between the surface are of aside portion 41, 51 of the physical surface and the surface area of aside portion 43, 53 of the sheath. The surface area of a horizontalportion is unchanged. For example, if the protrusion is a hexagonalcolumn, the surface area of the side portion is calculated by theequation of the width (a distance between opposing side surfaces)×tan30°×6 faces×height. In FIG. 14( a), when a sheath is formed, the outerwidth increases, thereby increasing the surface are of the side portion.In contrast, in FIG. 14( b), the inner width decreases, therebydecreasing the surface area of the side portion. Thus, the convexstructure is preferred to the concave structure. When the convexstructure is constituted by multiple concentric rings such as thoseindicated in FIGS. 13( a)-(c), the surface are of the side portionsnearly or substantially remains the same (this is because this structurecan be considered to be a concave structure). In any event, as long asthe structure is a convex structure, the surface area of the sideportion of a sheath is nearly or substantially equal to or greater thanthat of the physical surface.

For example, if the protrusions are hexagonal columns having a height of3-9 mm and a width of 3 mm and provided at a pitch of 6 mm, the physicalsurface area is increased by about 72% to about 216%. If the thicknessof a sheath formed over the physical surface is 0.5 mm, the extendedsurface area is increased by about 97% to about 292%. If the thicknessof a sheath formed over the physical surface is 1.0 mm, the extendedsurface area is increased by about 121% to about 365%.

In the above, the surface area increases in the case of convexstructures as long as a sheath formed over one protrusion and anothersheath formed over another protrusion do not merge, regardless of howthick the sheath actually is. If adjoining sheathes merge, a surfacearea no longer exists. Thus, a distance between adjoining protrusions ispreferably greater than twice the thickness of a sheath. Typically, thethickness of a sheath may be about 0.5 mm to about 1.0 mm, and thus, adistance between adjoining protrusions may be about 1 mm or more(including 2 mm, 3 mm, 5 mm, 10, and any numbers therebetween). Thesheath thickness approach is a theory and is not intended to limit thepresent invention.

In the above, the surface area of the physical surface increases, andthe surface are of the sheath further increases, and it may contributeto excellent controllability or operability. Further, in at least oneembodiment, the protrusions are discontinuous, and thus, a plasma maynot be confined between the protrusions. When a plasma is confined to aconcave portion in a structure such as those indicated in U.S. Pat. No.4,854,263, the contour of the concave portion is transferred on a filmdepositing on a substrate. For example, a portion on the filmcorresponding to the concave portion tends to have a thickness greaterthan that of the remaining portion. This can be observed by eye (colordifference can be observed) or can be determined by measuring thethickness of the film at several spots. The plasma confinement is atheory and is not intended to restrict the present invention.

The protrusions may comprise multiple truncated pyramids, prismaticcolumns, cones, or cylindrical columns or any other suitable shapes(e.g., FIGS. 2( a)-(c) and 3(a)-(c)). The protrusions may have anembankment shape (e.g., FIGS. 13( a)-(c)). In these figures, a basesurface (e.g., 23, 23′, 203) has multiple apertures (e.g., 21, 21′, 201)for passing a gas therethrough, and multiple protrusions (e.g., 22, 22′,202) each separately protrude from the base surface and are dispersedamong the apertures.

A width of each protrusion may be larger than a diameter of eachaperture by about 5% to 1000% (including 10%, 20%, 50%, 100%, 500%, andany numbers therebetween), depending on the distribution pattern of theapertures and the protrusions. The width of each protrusion may be about0.5 mm or more (including 1 mm, 2 mm, 3 mm, 5 mm, 10 mm, and any numberstherebetween) and a distance between adjoining protrusions is about 1 mmor more (including 2 mm, 3 mm, 5 mm, 10, and any numbers therebetween).The height of protrusions may be about 0.5 mm to 10.0 mm (including 1mm, 2 mm, 3 mm, 5 mm, 7 mm, and any numbers therebetween, preferably 3mm to 9 mm).

The number of the protrusions may be 4 to 5,000 (including 10, 50, 100,500, 1,000, 2,000, 3,000, and any numbers therebetween), depending onthe shape of the protrusion. When a column- or cone-type is used, theprotrusions may be more than half the number of the apertures. In anembodiment, the number of the protrusions may be 1, 2, 3, or 4 times thenumber of the apertures. The number of apertures may be 1,000 to 5,000(typically 3,200-4,200, in an embodiment, 1,900-3,000). The diameter ofthe aperture may be about 0.1 mm to 2.0 mm, typically 0.3 mm to 0.8 mm.

The distance between an aperture and a protrusion may be determinedbased on the above positional relationships. For example, when thedistance between adjoining protrusions is 2 mm, and the diameter of anaperture is 0.8 mm, the distance from the periphery of the aperture toone of the protrusions is 0.6 mm. In an embodiment, such a distance is0.6 mm or greater (including 0.8 mm, 1 mm, 1.5 mm, 2 mm, and any numberstherebetween).

In another embodiment, the present invention provides a shower plate forplasma CVD comprising: (i) a base surface; (ii) multiple protrusionsprotruding from the base surface, and (iii) multiple apertures forpassing a gas therethrough dispersed on a front face constituted by thebase surface and the protrusions, wherein a surface area of the basesurface and the protrusions is greater by at least 40% than a calculatedsurface area of the base surface if no protrusions are provided, andwherein a surface area when extending from the base surface and theprotrusions by a sheath generated by plasma exposure is nearly orsubstantially equal to or greater than the surface area of the basesurface and the protrusions.

In the above, the apertures may not be provided in the base surface butcan be provided in the protrusions (in top surfaces of the protrusions).Preferably, the apertures are dispersed on the base surface, and theprotrusions are dispersed among the apertures. As long as a surface areawhen extending from the base surface and the protrusions by a sheathgenerated by plasma exposure is nearly or substantially equal to orgreater than the surface area of the base surface and the protrusions,the protrusions can be formed integrally (multiple pieces are integratedsuch as multiple strands radically extending from a common center). Anyelements in the previous embodiment can be used in this embodiment aslong as application of such elements is feasible.

In another embodiment, the present invention provides a plasma CVDapparatus comprising: (a) a reaction chamber; (b) a showerhead providedin the chamber, which serves as an electrode and comprises any one ofthe shower plates of the foregoing and a body member to which the showerplate is attached; and (c) a susceptor provided in the chamber, whichserves as another electrode and is disposed parallel to the showerplate. The shower plate can be installed in various types of plasma CVDapparatuses. The shower plate can be attached to a shower body using afastening device such as screws, or can be formed integrally with ashower body. The shower plate can be made of aluminum or aluminum alloy,and can be surface-treated such as anodization (e.g., anodized oxidefilm).

In still another embodiment, the present invention provides a plasma CVDmethod comprising: (1) placing a substrate on a susceptor disposedparallel to any one of the shower plates of the foregoing; (2)introducing a reaction gas through the shower plate; (3) generating aplasma between the susceptor and the shower plate by applyingradio-frequency energy therebetween, wherein a sheath is formed over theshower plate, wherein a surface area of the sheath is nearly orsubstantially equal to or greater than a physical surface area of theshower plate; and (4) depositing a film on the substrate.

In yet another embodiment, the present invention provides a plasma CVDmethod comprising: (1) placing a substrate on a susceptor disposedparallel to any one of the shower plates of the foregoing; (2)introducing a reaction gas through the shower plate; (3) generating aplasma between the susceptor and the shower plate by applyingradio-frequency energy therebetween, wherein a sheath is formed over theshower plate, wherein a surface area of the sheath is nearly orsubstantially equal to or greater than a physical surface area of theshower plate; and (4) depositing a film on the substrate.

In the above, the film may be selected from the group consisting ofsilicon nitride, silicon oxide, silicon oxynitride,low-dielectric-constant fluorine-doped silicon oxide, andlow-dielectric-constant carbon-doped silicon oxide films.

In all of the aforesaid embodiments, any element used in an embodimentcan interchangeably be used in another embodiment unless such areplacement is not feasible or causes adverse effect. Further, thepresent invention can equally be applied to apparatuses and methods.

The present invention will be explained with reference to preferredembodiments. However, the preferred embodiments are not intended tolimit the present invention. An embodiment of the present invention isdescribed in detail below with reference to drawings attached.

FIG. 1 shows a schematic view of one embodiment of the plasma CVDapparatus according to the present invention. This plasma CVD apparatus10 comprises a vacuum (reaction) chamber 11, a first electrode 12 beingprovided at the top of the vacuum chamber 11 and insulated from thevacuum chamber 11, a second electrode 13 being provided inside thevacuum chamber 11 substantially parallel to the first electrode 12, andRF power sources 14 and 15 connected to the first electrode.

The vacuum chamber 11 has an opening at its lower portion and comprisesan exhaust port 111 connected to an exhaust pump not shown.Additionally, the vacuum chamber 11 is grounded.

The first electrode 12 has a hollow structure, and an upper tubularportion comprises a gas inlet port 121 connected to a gas line (notshown). Additionally, on a bottom face of the first electrode, a showerplate 122 is removably attached. In the shower plate 122, many gas inletholes (pores) are formed so that a jet of a source gas introduced fromthe gas inlet port 121 is emitted from the holes toward the secondelectrode 13. Additionally, on the front face of the shower plate 122(the undersurface of the shower plate 122 in FIG. 1), protrusionsdescribed in detail later are formed. By removably attaching the showerplate 122, maintenance becomes easier and part replacement-related costscan be curtailed.

The second electrode 13 has a heater 131 and a susceptor 132 providedthereon. The susceptor 132 is disposed substantially parallel to theshower plate 122 and holds a workpiece 16 being placed on its uppersurface.

A method for forming a thin film on a workpiece using the plasma CVDapparatus shown in FIG. 1 is described in detail below, although thepresent invention is not limited thereto.

In at least one embodiment, first, the workpiece 16 is placed on thesusceptor 132. Inside the vacuum chamber 11 is evacuated to a givenpressure by an exhaust pump connected to the exhaust port 111.

The workpiece is heated to a given temperature (e.g., 150-450° C.) bythe heater 131, and is kept at the given temperature.

A source gas is introduced from the gas inlet port 112 into the vacuumchamber 11, and at the same time, RF voltage is applied to the firstelectrode 12 using the RF power source 14. If necessary, RF voltage fromthe second RF power source 15 is applied to the first electrode 12 byoverlaying it on another. The second electrode 13 is grounded, or agiven bias voltage is applied. As a result, discharge occurs between thefirst electrode 12 and the second electrode 13, and the source gas goesinto the plasma state. Thus, a plasma reaction field is formed in thevicinity of the workpiece 16, and a thin film is formed on a surface ofthe workpiece 16.

A type and properties of a thin film formed on the surface of theworkpiece 16 depend on a type and flow rate of a source gas, atemperature of a workpiece, a frequency and swing of RF voltage suppliedfrom RF power sources 14 and 15, plasma spatial distribution andelectric potential distribution.

In order to form silicon nitride films, silane may be used as asilicon-containing source gas, and nitrogen and/or ammonia may be usedas a nitriding gas. In order to form silicon oxide films (USG: UndopedSilicate Glass films), silane or TEOS (tetra-ethyl-ortho-silicate) maybe used as a silicon-containing source gas; as an oxidized gas, nitrousoxide may be used when silane is used, or oxygen may be used when TEOSis used. In order to form B (boron)-doped silicon oxide films (BSG:Boro-Silicate Grass films), in addition to a source gas used for thesilicon oxide films, diborane may be used as a doping gas. In order toform P (phosphorus)-doped silicon oxide films (PSG: Phospho-SilicateGrass films), in addition to a source gas used for the silicon oxidefilms, phosphine may be used as a doping gas. In order to form B andP-doped silicon oxide films (BPSG: Boro-Phospho Silicate Grass films),in addition to a source gas used for the silicon oxide films, bothdiborane and phosphine may be used. In order to form silicon oxynitridefilms, silane may be used as a silicon-containing source gas, nitrogenand/or ammonia as a nitriding gas, and nitrous oxide may be used asoxidized gas. In order to form low-dielectric-constant fluorine-dopedsilicon oxide films, TEOS/oxygen/CF₄-containing gas, or silane/nitrousoxide/SiF₄-containing gas, etc. may be used. In order to formlow-dielectric-constant carbon-doped silicon oxide films,silicon-containing hydrocarbon having multiple alkoxy groups and Ar(argon), and/or He (helium) may be used. According to circumstances,oxygen, nitrous oxide, carbon dioxide or alcohol, etc. may be used.

In order to control plasma spatial distribution and electric potentialdistribution inside the vacuum chamber 11, protrusions are formed on thefront face of the shower plate 122.

FIGS. 2( a)-(c) show one example of the shower plate 122. FIGS. 2(a)-(c) are a partial cross section seen from obliquely upward, apartial longitudinal cross section, and a partial bottom view,respectively, showing the shower plate 122. Additionally, the showerplate 122 is normally disk-shaped.

As shown in FIGS. 2( a) and (b), the reverse face (the upper surface inthe figures) of the shower plate 122 is a plane surface, and many gasinlet holes (pores) 21 reaching the front face (the undersurface in thefigures) are formed with an arrangement. Additionally, in the front face(the undersurface in the figures) of the shower plate 122, manyprotrusions 22 are formed with an arrangement. Protrusions 22 aredisposed so as to avoid pores 21 (so as to be apart from the pores 21 ata given distance). Therefore, the plane-surface portion 23 existssurrounding the pores 21. In other words, the protrusions 22 are formedso as to protrude downward from the plane-surface portion 23 surroundingthe pores 21.

A size (an aperture diameter) and arrangement of the pores 21 aredetermined so as to non-formalize a distribution of a source gasintroduced into the vacuum chamber (at least in the vicinity of theupper surface of a workpiece). Additionally, according to a size andarrangement of the pores 21 determined, a shape, size and arrangement ofprotrusions 22 can be determined so as to achieve uniform plasma spatialdistribution and electric potential distribution. A size and arrangementof the pores 21 and a shape, size and arrangement of the protrusions 22are not limited to those shown in FIGS. 2( a)-(c), and may be changedappropriately. For example, they can be changed to those shown in FIGS.3( a), (b), and (c).

Protrusions 22 shown in FIGS. 2( a)-(c) are hexagonal-column-shaped;protrusions 22′ shown in FIGS. 3( a)-(c) are truncated-pyramid-shaped.These shapes are used because forming them by machine work is easy;other shapes, e.g., cylindrical, conical, hemispheric, etc. can also beused. Additionally, a shape can be any polyangular column shapes or anypolyangular pyramid shapes. Furthermore, multiple protrusions having anembankment shape (a mesa shape) of a given width may also be used bydisposing them parallel, by a lattice-like arrangement, orconcentrically. Additionally, angular portions may be chamfered.

A diameter of the protrusion 22 (22′) may be larger than a diameter ofthe pore 21 (21′). In other words, a base area of respective protrusions22 (22′) may be larger than an area of a circle of diameter 1 mm.Additionally, a distance between adjoining protrusions 22 should betwice or more a sheath thickness, e.g., 2 mm or more, so as to generateplasma between the protrusions. As to a length of the protrusion 22,although approximately twice its diameter may be machine work limitswhen it is formed by machine work, the length should be, e.g., 0.5 mm orlonger. As to the number of protrusions 22, ¼ or more the number of gasinlet pores is preferable; ½ or more is more preferable.

In the cases of protrusions having shapes shown in FIGS. 2( a)-(c) andFIGS. 3( a)-(c) respectively, they are formed in the same way as theabove-mentioned. However, in the case of a protrusion having anembankment shape, the number of the protrusions may substantially beless than the number of the gas inlet holes 22.

By forming protrusions 22 (22′, etc.) on the front face of the showerplate 122, its surface area, particularly its surface area with sheathtaken into consideration, is increased; and plasma is formed betweenadjoining protrusions 22 as well. It may not mean that plasma beingformed between adjoining protrusions 22 is remarkably stronger thanplasma being formed in other areas, but it may mean that plasma spatialdistribution is improved by plasma being formed between adjoiningprotrusions 22 as compared with the related art. As a result, forexample, when a silicon nitride film is formed, controllability overinternal stress of a film formed can be improved as compared with therelated art; hence both improved controllability and decreased hydrogenconcentration in the film can be achieved. Additionally, by an increasedsurface area of the shower plate 122, electric potential distributioncan be improved and DC voltage Vdc and power source peak voltage Vppapplied to the first electrode 12 can be lowered. As a result,occurrence of abnormal discharge can be suppressed; hence damage to thefirst electrode and plasma damage to workpieces can be prevented ordecreased. For example, when a low-dielectric-constant carbon-dopedsilicon oxide film is formed, with the related art, abnormal dischargeoccurred relatively frequently because high RF power is applied. In theplasma CVD apparatus according to this embodiment, occurrence ofabnormal discharge is hardly seen.

Additionally, although, in at least one embodiment, the shower plate isremovably attached, a shower plate may be formed as one with the firstelectrode or may be fixed with the first electrode.

The present invention will be explained by examples. However, thepresent invention is not limited to the examples.

Example 1

Thin film formation was conducted using the plasma CVD apparatuscomprising the shower plate 22 shown in FIG. 2; and properties of thinfilms formed were measured (Examples 1-1 to 1-5). Additionally, ascomparative examples, thin film formation was conducted using a plasmaCVD apparatus comprising a shower plate similar to the shower platedescribed in U.S. Pat. No. 4,854,263; and properties of a thin filmformed were measured. Specifications of the shower plates used are shownin Table 1 below. In Table 1, a rate of surface area increase is a rateof surface area increase as against a surface area of a tabular showerplate without protrusions or concave portions.

TABLE 1 Example 1 Comparative Example Configuration Hexagonal Concavecolumn Height/depth 3.7 mm 3.8 mm Width (face to face)/diameter   3 mm  3 mm Pitch   6 mm 4.2 mm The number 2,233 4,005 Increase of surfacearea Actual surface area 89.8% 152.8% 0.5 mm sheath considered 119.8%101.1% 1.0 mm sheath considered 149.7% 50.6%

Example 1-1

Film type: Low-deposition-rate silicon nitride film (Deposition rate<200nm/min. (e.g., 160-190 nm/min.))

Deposition Conditions:

Source gas 1: Silane (50-150 sccm, preferably 65-95 sccm)

Source gas 2: Ammonia (20-80 sccm, preferably 25-60 sccm)

Source gas 3: Nitrogen (5000-10000 sccm, preferably 7,500-10,000 sccm)

First RF power source (HRF): 13.56 MHz (1-1. 5 W/cm²—Anode reference)

Second RF power source (LRF): 400 kHz (0 W/cm²)

Pressure: 450-600 Pa (preferably 465-560 Pa)

Temperature: 300-400° C. (preferably 380-400° C.)

Workpiece: Diameter 300 mm silicon substrate

Cleaning frequency: Single wafer

Under the above-mentioned conditions, measurement results of propertiesof a thin film formed using the shower plate according to thisembodiment of the present invention are shown in FIG. 4; measurementresults of properties of a thin film formed using the shower headaccording to the related art are shown in FIG. 5.

When a low-deposition-rate silicon nitride thin film is formed, adesired value for the film's internal stress is about −100 MPa to about−200 MPa. When measurement results in FIG. 4 and FIG. 5 are compared, itis seen that using the shower plate according to this embodiment of thepresent invention, there was less change in the film's internal stressas against change in the output power of the first RF power source;hence control of the inner stress is easier.

Additionally, using the Fourier transform infrared spectroscopy, peakareas of Si—H bonds (in the neighborhood of 2100 cm⁻¹), N—H bonds (inthe neighborhood of 3300 cm⁻¹) and Si—N bonds (in the neighborhood of800 cm⁻¹) are obtained; using the ratio obtained, evaluation of hydrogenconcentration in the films was performed, i.e., Si—H (%)=(Si—H bond peakarea/Si—N bond peak area)×100%, N—H (%)=(N—H bond peak area/Si—N bondpeak area)×100% were obtained. As a result, it was confirmed that thehydrogen concentration in the film of the thin film formed using theshower plate according this embodiment of the present invention wasSi—H<2% (about 1.8%).

Low-deposition-rate silicon nitride films are desired to comprise bothinternal stress of about −100 MPa to about −200 MPa and low hydrogenconcentration in the film (Si—H<2% (about 1.8%)). As described above,forming a film possessing both desired properties was achieved using theshower plate according this embodiment of the present invention.

Additionally, in the comparative example, it was found that a surfacepattern of the first electrode had been transferred to a thicknessdistribution of the film formed. In other words, film thickness was notuniform.

Example 1-2

Film type: Low-deposition-rate silicon nitride thin film (Depositionrate<200 nm/min. (e.g., 160-190 nm/min.))

Deposition Conditions:

Source gas 1: Silane (50-150 sccm, preferably 65-95 sccm)

Source gas 2: Ammonia (20-80 sccm, preferably 25-60 sccm)

Source gas 3: Nitrogen (5000-10000 sccm, preferably 7,500-10,000 sccm)

First RF power source (HRF): 13.56 MHz (0.72 W/cm² fixed—Anodereference)

Second RF power source (LRF): 400 kHz (0.05-0.2 W/cm²—Anode reference)

Pressure: 450-600 Pa (preferably 465-560 Pa)

Temperature: 300-400° C. (preferably 380-400° C.)

Workpiece: Diameter 300 mm silicon substrate

Cleaning frequency: Single wafer

In this example, except that output of the first RF power source wasfixed and that output of the second RF power source was changed, thesame conditions as used for Example 1-1 were used. Under theabove-mentioned conditions, measurement results of properties of a thinfilm formed using the shower plate according to this embodiment of thepresent invention are shown in FIG. 6; measurement results of propertiesof a thin film formed using the shower head according to the related artare shown in FIG. 7.

As mentioned in Example 1-1 as well, when a low-deposition-rate siliconnitride thin film is formed, a desired value of the film's internalstress is about −100 MPa to about −200 MPa. When the measurement resultsshown in FIG. 6 and FIG. 7 are compared, it is seen that using theshower plate according to this embodiment of the present invention,there was less change in the film's internal stress as against change inthe output power of the second RF power source; hence control of theinner stress is easier.

Low-deposition-rate silicon nitride thin films are desired to compriseboth internal stress of about −100 MPa to about −200 MPa and lowhydrogen concentration in the film (Si—H<2% (about 1.8%)). Using theshower plate according this embodiment of the present invention, it wasconfirmed by the separate measurement result that forming a filmpossessing both desired properties was achieved.

Additionally, in the comparative example, it was found that a surfacepattern of the first electrode had been transferred to a thicknessdistribution of the film formed. In other words, film thickness was notuniform.

Example 1-3

Film type: High-deposition-rate silicon nitride thin film (Depositionrate<500 nm/min. (e.g., 550-650 nm/min.))

Deposition Conditions:

Source gas 1: Silane (300-500 sccm, preferably 360-440 sccm)

Source gas 2: Ammonia (2000-3000 sccm)

Source gas 3: Nitrogen (500-2500 sccm)

First RF power source (HRF): 13.56 MHz (0.8-1.3 W/cm²—Anode reference)

Second RF power source (LRF): 400 kHz (0.5 W/cm² fixed—Anode reference)

Pressure: 450-600 Pa (preferably 465-560 Pa)

Temperature: 300-400° C. (preferably 380-400° C.)

Workpiece: Diameter 300 mm silicon substrate

Cleaning frequency: Single wafer

Under the above-mentioned conditions, measurement results of propertiesof a thin film formed using the shower plate according to thisembodiment of the present invention are shown in FIG. 8; measurementresults of properties of a thin film formed using the shower headaccording to the related art are shown in FIG. 9.

When high-deposition-rate silicon nitride films are formed as well,similarly to low-deposition-rate silicon nitride films, a desired valueof the films' internal stress is about −100 MPa to about −200 MPa. Whenmeasurement results in FIG. 8 and FIG. 9 are compared, it is seen thatusing the shower plate according this embodiment of the presentinvention, there was less change in the film's internal stress asagainst change in the output power of the first RF power source; hencecontrol of the inner stress is easier.

High-deposition-rate silicon nitride thin films are desired to compriseboth internal stress of about −100 MPa to about −200 MPa and lowhydrogen concentration in the film (Si—H<5% (e.g., 3.5-4.8%)). Using theshower plate according this embodiment of the present invention, it wasconfirmed by the separate measurement result that forming a filmpossessing both desired properties was achieved.

Additionally, in the comparative example, it was found that a surfacepattern of the first electrode had been transferred to a thicknessdistribution of the film formed (observed by eye). In other words, filmthickness was not uniform.

Example 1-4

Film type: Low-dielectric-constant C-doped silicon oxide film

Deposition Conditions:

Source gas: DM-DMOS (Dimethyl-dimethoxysilane) (200 sccm)

Additive gas: He (400 sccm)

First RF power source (HRF): 27.12 MHz (3.0 W/cm²—Anode reference)

Second RF power source (LRF): 400 kHz (0.1 W/cm²—Anode reference)

Pressure: 450-600 Pa (preferably 465-560 Pa)

Temperature: 300-400° C. (preferably 380-400° C.)

Workpiece: Diameter 300 mm silicon substrate

Cleaning frequency: Single wafer

Under the above-mentioned conditions, film deposition was conducted on100 pieces of silicon substrates consecutively. Under theabove-mentioned conditions, abnormal discharge frequently occurs if atabular shower plate is used. Using the shower plate according to thisembodiment of the present invention, abnormal discharge never occurred.

Additionally, in the comparative example, it was found that a surfacepattern of the first electrode had been transferred to a thicknessdistribution of the film formed (observed by eye). In other words, filmthickness was not uniform.

Example 1-5

Film type: Silicon oxide films (USG, BPSG, PSG, BSG), silicon oxynitridefilm, low-dielectric-constant F-doped silicon oxide film

It was confirmed that using the shower plate according to thisembodiment of the present invention, respective thin films were able tobe formed without problems. As film deposition conditions for these filmtypes are relatively loose (e.g., 13.56 MHz, 0.5 W/cm²—Anode reference)and these films' parameter-dependence is low, there was no remarkabledifference observed between the films formed using the shower plateaccording to this embodiment of the present invention and the filmsformed using the shower plate of the related art.

Example 2

Using a plasma CVD apparatus comprising the shower plate 22′ shown inFIG. 3, film deposition was conducted, and properties of the filmsformed were measured (Examples 2-1 to 2-5). Specifications of the showerplate used are shown in Table 2 below.

TABLE 2 Example 2 Configuration Truncated pyramid (four-sided) Height 6mm Width (face to face) 3 mm Pitch 6 mm The number 2,593 Increase ofsurface area Actual surface area 107.2% 0.5 mm sheath considered 153.6%1.0 mm sheath considered 199.9%

Example 2-1

Film type: Low-deposition-rate silicon nitride thin film (Depositionrate<200 nm/min. (e.g., 160-190 nm/min.))

Deposition conditions: The same as used in Example 1-1

Properties of a film formed using the shower plate according to thisembodiment of the present invention under the above-mentioned conditionswere measured; measurement results are shown in FIG. 10. As is evidentby comparison with the measurement results shown in FIG. 5, using theshower plate according to this embodiment of the present invention,there was less change in the film's internal stress as against change inthe output power of the first RF power source; hence control of theinner stress is easier.

Additionally, as a result of evaluating hydrogen concentration in thefilm using the same method as used with Example 1-1, it was confirmedthat the film's hydrogen concentration in the film was Si—H<2% (about1.8%). In other words, using the shower plate according to thisembodiment of the present invention as well, forming a film possessingboth desired film properties for the low-deposition-rate silicon nitridethin film, which are the internal stress of about −100 MPa to about −200MPa and low hydrogen concentration in the film (Si—H<2% (about 1.8%)),was achieved.

Example 2-2

Film type: Low-deposition-rate silicon nitride thin film (Depositionrate<200 nm/min. (e.g., 160-190 nm/min.))

Deposition conditions: The same as used in Example 1-2

Properties of a film formed using the shower plate according to thisembodiment of the present invention under the above-mentioned conditionswere measured; measurement results are shown in FIG. 11.

In the same way as in Example 1-2, as compared with the measurementresults shown in FIG. 7, it is seen that controllability is better thanusing the shower plate of the related art. Additionally, it wasconfirmed that forming a film possessing both internal stress of about−100 MPa to about −200 MPa and low hydrogen concentration in the film(Si—H<2% (about 1.8%)) was achieved by using the shower plate accordingto this embodiment of the present invention.

Example 2-3

Film type: High-deposition-rate silicon nitride thin film (Depositionrate<500 nm/min. (e.g., 550-650 nm/min.))

Deposition conditions: The same as used in Example 1-3

Properties of a film formed using the shower plate according to thisembodiment of the present invention under the above-mentioned conditionswere measured; measurement results are shown in FIG. 12.

As compared with the measurement results shown in FIG. 9, it is seenthat controllability is better than using the shower plate of therelated art.

Additionally, using the shower plate according to this embodiment of thepresent invention, it was confirmed that forming a film possessing bothdesired film properties for the high-deposition-rate silicon nitridethin film, which are the internal stress of about −100 MPa to about −200MPa and low hydrogen concentration in the film (Si—H<5% (e.g.,3.5-4.8%)), was achieved.

Example 2-4

Film type: Low-dielectric-constant C-doped silicon oxide film

Deposition conditions: The same as used in Example 1-4

In the same way as was in Example 1-4, film deposition was conducted on100 pieces of silicon substrates consecutively. Abnormal discharge neveroccurred.

Example 2-5

Film type: Silicon oxide films (USG, BPSG, PSG, BSG), silicon oxynitridefilm, low-dielectric-constant fluorine-doped silicon oxide film

It was confirmed that using the shower plate according to thisembodiment of the present invention, respective thin films were able tobe formed without problems.

The present invention includes the above mentioned embodiments and othervarious embodiments including the following:

1) A shower plate having multiple gas inlet holes being formed with anarrangement and used in a plasma CVD apparatus, which is characterizedin that a plane-surface portion surrounding apertures of multiple gasinlet holes and protrusions protruding from the plane-surface portionare formed on the front face of the shower plate.

2) A plasma CVD apparatus provided with a shower plate having multiplegas inlet holes being formed with an arrangement and used in a plasmaCVD apparatus, which is characterized in that a plane-surface portionsurrounding the apertures of multiple gas inlet holes and protrusionsprotruding from the plane-surface portion are formed on the front faceof the shower plate.

3) A plasma CVD method for forming a thin film on a workpiece using aplasma CVD apparatus provided with a shower plate having multiple gasinlet holes being formed with an arrangement and used in a plasma CVDapparatus, which is characterized in that a plane-surface portionsurrounding the apertures of multiple gas inlet holes and protrusionsprotruding from the plane-surface portion are formed on the front faceof the shower plate, wherein the plasma CVD method is characterized bybeing adapted to form any one of silicon nitride, silicon oxide, siliconoxynitride, low-dielectric-constant fluorine-doped silicon oxide, andlow-dielectric-constant carbon-doped silicon oxide films as the thinfilm by introducing source gases via the shower plate and by applyingradio frequency power to the shower plate.

4) A thin film, which is characterized by having been formed on aworkpiece using a plasma CVD apparatus provided with a shower platehaving multiple gas inlet holes being formed with an arrangement andused in a plasma CVD apparatus which is characterized in that aplane-surface portion surrounding the apertures of multiple gas inletholes and protrusions protruding from the plane-surface portion areformed on the front face of the shower plate, is obtained.

According to at least one of the above embodiments of the presentinvention, by forming a plane-surface portion surrounding the aperturesof multiple gas inlet holes and protrusions protruding from theplane-surface portion on the front face of a shower plate, and using aplasma CVD apparatus using the shower plate, a thin film can be formedstably with excellent controllability.

The present application claims priority to Japanese Patent ApplicationNo. 2004-044854, filed Feb. 20, 2004, the disclosure of which isincorporated herein by reference in its entirety.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

1. A shower plate for a plasma CVD apparatus comprising a firstelectrode with a shower plate having a first face that faces a secondelectrode, wherein the first face of the shower plate includes: anexterior base surface facing the second electrode and having multipleapertures for passing a gas therethrough, each aperture extending fromthe exterior base surface to a face other than the exterior basesurface; and multiple discontinuous protrusions each having the samesize and separately protruding in a direction toward the secondelectrode and extending from the exterior base surface along thethickness direction of the shower plate and being dispersed among theapertures, wherein a tip of each protrusion faces the second electrodeaway from the exterior base surface having the apertures, a distancebetween any one of the protrusions and any one of the apertures adjacentto each other is smaller than a distance between the protrusion and anyprotrusion adjacent to the protrusion, the number of the apertures isgreater than the number of the protrusions.
 2. The shower plateaccording to claim 1, wherein a surface area of the base surface and theprotrusions is greater by at least 40% than a calculated surface area ofthe base surface if no protrusions are provided.
 3. The shower plateaccording to claim 1, wherein a surface area when extending from thebase surface and the protrusions by a sheath generated by plasmaexposure is nearly or substantially equal to or greater than the surfacearea of the base surface and the protrusions.
 4. The shower plateaccording to claim 1, wherein the base surface is constituted by a planesurface.
 5. The shower plate according to claim 1, wherein a width ofeach protrusion is larger than a diameter of each aperture.
 6. Theshower plate according to claim 1, wherein the width of each protrusionis about 1 mm or more and a distance between adjoining protrusions isabout 2 mm or more.
 7. The shower plate according to claim 1, whereinthe number of the protrusions is more than half the number of theapertures.
 8. The shower plate according to claim 1, wherein any one ofthe protrusions is equidistant from the apertures adjacent to theprotrusion as viewed from above with reference to the base surface. 9.The shower plate according to claim 8, wherein each protrusion hasprotrusions adjacent to and equidistant from the protrusion and arrangedat points of a hexagon or a quadrilateral as viewed from above withreference to the base surface.
 10. The shower plate according to claim8, wherein each protrusion has apertures adjacent to and equidistantfrom the protrusion and arranged at points of a hexagon or aquadrilateral as viewed from above with reference to the base surface.11. The shower plate according to claim 8, wherein each protrusion hasprotrusions adjacent to and equidistant from the protrusion and arrangedat points of a hexagon as viewed from above with reference to the basesurface, and has apertures adjacent to and equidistant from theprotrusion and arranged at points of a hexagon as viewed from above withreference to the base surface.
 12. The shower plate according to claim1, wherein the shower plate is made of anodized aluminum.
 13. The showerplate according to claim 1, wherein the protrusions are made of multipleconvex truncated pyramids, convex prismatic columns, or convex cones.